An important example is when Microsoft launches the web suite for Office 2010 and it potentially runs slowly in older IE versions.
What will also be interesting is how far their backwards compatability travels. Will Microsoft signal the death of IE6 by not supporting their own software in their web Office suite? Unlikely, but interesting regardless.
Interesting question. On the one hand, they could give IT shops a reason to upgrade to IE8. The main holdouts on IE6 are corporations with legacy apps.
On the other hand, such an requirement would give the same shops a reason not to upgrade to Office 2010 at all.
If I know MS, they probably created JavaScript callable stubs for the .NET components already in the OS. This is the same way JScript cheated by calling ActiveX components that shipped with the OS and Office. I would be surprised if MS really embraced web standards. Or we can expect a portable Silverlight runtime which brings ActiveX to non-MS platforms (like Flash, but from an actual tool vendor. Adobe is struggling being Sun and Pixar at the same time; they're speaking to a wide audience with diverging interests)
What will also be interesting is how far their backwards compatability travels. Will Microsoft signal the death of IE6 by not supporting their own software in their web Office suite? Unlikely, but interesting regardless.